A magnetic sensor of the above-mentioned type is represented in perspective and exploded in FIG. 1 which is appended to the present patent application. Designated overall by the general numerical reference 1, this magnetic sensor is mounted on the surface 2 of a semiconductor substrate 4 of a substantially parallelepiped shape. An electronic circuit (not shown) associated with the magnetic sensor is produced by CMOS integration on the large upper surface 2 of the semiconductor substrate 4.
The magnetic sensor 1 comprises a flat excitation coil 6 which is formed in a metallic layer applied to the face 2 of the substrate 4 in the course of the CMOS integration process. The coil 6 has an exterior perimeter formed by its external wrap 60 of a substantially square shape. The other wraps 62 to 68 of this excitation coil 6 are disposed in a concentric manner with respect to the external wrap 60. Likewise of a square shape, the wraps 62 to 68 are of progressively decreasing dimensions, as is visible in FIG. 1.
A ferromagnetic core 8 is mounted, typically by gluing, above the excitation coil 6. This ferromagnetic core 8 is produced from a band of amorphous magnetic material which is currently available commercially.
As can be seen in FIG. 1, the magnetic core 8 has the shape of a cross which coincides with the two diagonals of the square defined by the external wrap 60 of the excitation coil 6. One can therefore measure two perpendicular components H1 and H2 of the external magnetic field HEXT, these two components being respectively directed according to the orthogonal branches 80 and 82 of the core 8. The component H1 of the external magnetic field HEXT is thus measured by the branch 80 of the core 8, whilst the component H2 is measured by its perpendicular branch 82.
The detection of the external magnetic field HEXT is accomplished by means of two pairs of coplanar detection coils 10, 12 and 14, 16. The two first coils 10 and 12, applied by CMOS technology on the upper surface 2 of the semiconductor substrate 4, are mounted in series according to a differential arrangement. Disposed under the flat excitation coil 6 or in the same plane as the latter, these two coils 10 and 12 are each positioned facing one of the free ends of the branch 80 of the ferromagnetic core 8. This first pair of coils 10, 12 has therefore the role of detecting the component H1 of the exterior magnetic field HEXT.
The two other detector coils 14 and 16 are identical to the two coils 10 and 12 described previously. Likewise mounted in series according to a differential arrangement, these two detector coils 14, 16 are each disposed facing one of the free ends of the second branch 82 of the ferromagnetic core 8. This second pair of coils 14, 16 has therefore the role of detecting the component H2 of the exterior magnetic field HEXT.
The magnetic sensors of the above-described type are in particular intended for equipping magnetometers for detecting, in a plane parallel to the plane of the detection coils, magnetic fields of low to very low value, for example for medical applications. These magnetometers are therefore produced preferably according to CMOS integration techniques, their associated electronic circuits being integrated in the substrate on which the sensors are produced.
The production of such devices for detection and measurement of magnetic fields poses a great problem which, as far as the applicant knows, has not to this day been resolved in a satisfactory fashion. In fact, the electronic circuits associated with magnetic sensors are produced by CMOS technology which comprises a collection of steps for designing and producing electronic components which, today, are remarkably well mastered and allow reliable and cheap devices to be produced in large numbers.
On the other hand, things are different with the production of magnetic sensors associated with the electronic circuits mentioned above. As described above, these magnetic sensors comprise in particular an amorphous ferromagnetic core. Now, none of the currently available techniques for producing semiconductor devices allows components with an amorphous structure to be produced. Amongst these techniques, there can be cited in particular vapour phase deposition, better known with its Anglo-Saxon title “chemical vapour deposition” (CVD), which comprises evaporating in a vacuum a metal which is sublimated by heating in order to form, for example, an oxide or nitride layer with a chemical reaction produced by an appropriate gas. Another technique, known by the title of electro-deposition or galvanoplasty, comprises forming a metallic layer on an item by electrolysis and applies to dissolved or molten compounds which are dissociable into two types of ions ensuring the passage of the current by their displacement, the positive ions being directed towards the cathode and the negative ions towards the anode.
Hence, the techniques for producing CMOS integrated circuits only allow production of components with an ordered crystalline structure, and they are unable to propose replacement solutions for developing bodies with an amorphous structure, i.e. not having a crystal lattice. In any case, certain techniques are known which allow a layer of amorphous material to be deposited on the surface of a substrate. These techniques only permit however deposition of materials which have a simple chemical composition formed by a single component. For more complex products, like a magnetic material which comprises a plurality of components, nothing has been able to be proposed.
The technique reserved by the applicant for producing magnetic sensors, such as described in the patent application EP 1 052 519 mentioned above, comprises therefore producing firstly, on a semiconductor board, a series of electronic circuits, then sawing this board in order to provide a plurality of individual electronic circuits, and finally gluing on these individual circuits bands of amorphous magnetic material which, after photolithography and etching, will form the ferromagnetic cores.
It will be readily understood that such a technique, if it can be used at the experimental stage, is in no way applicable on an industrial scale where very large quantities of components must be able to be produced rapidly and at low cost.
The object of the present invention is to eliminate the disadvantages mentioned above and also others by proposing a method for producing in series and at the same time reliably and cheaply, magnetic sensors, the zone which is sensitive to the external magnetic field of which is produced in an amorphous magnetic material.